This invention relates to a contour cutting machine for the cutting of objects, such as e.g. blocks made from foamed plastic, wadding, synthetic material, rubber or cork, comprising a rotating endless bandknife.
A contour cutting machine according to the precharacterizing part of claim 1 is known from DE 23 29 238 C2. This machine comprises a table for receiving the workpiece block, and a support arranged for vertical movement relative to the table. On the support, vertically movable carriages are arranged to both sides of the table. An endless bandknife is arranged to rotate around a plurality of bandknife pulleys, wherein respectively one bandknife pulley is located on one of the movable carriages and the rest of the bandknife pulleys are fixed to the machine. The bandknife is guided in a closed loop, with a first portion of the loop arranged between the two vertically adjustable bandknife pulleys while forming a cutting strand in this region. The first loop portion is of a rectangular shape and has the second loop portion extending therefrom which is guided around a fifth bandknife pulley and is used for a length compensation of the bandknife in case of different cutting heights. The fifth bandknife pulley is engaged by a tensioning device for setting the tension of the bandknife. On both end portions of the cutting strand, the respective carriages are provided with rotating devices for rotating the plane of the bandknife so as to change the cutting angle. In this bandknife guiding configuration comprising two loop portions merging into each other, the bandknife has its inner side contacting a total of four bandknife pulleys and has its outer side contacting one of the bandknife pulleys. As a result, the bandknife during its continuous circulation is subjected to varying alternating bending stresses which are directed both towards its inner face and towards its outer face. Due to these alternating bending stresses in combination with the torsional stresses generated by the rotating devices and the tensioning of the bandknife in the longitudinal direction, the bandknife suffers considerable mechanical stresses so that the bandknife may undesirably break and has a reduced lifespan.
A contour cutting machine comprising a cutting wire with a similar cutting wire guiding configuration is known from GB 2 206 521 A. In this known machine, a cutting wire is guided to follow mutually contacting loops, thereby running around pulleys deflecting the cutting wire alternately into one direction and a direction opposite thereto.
EP-0 390 939 B1 discloses a contour cutting machine wherein the bandknife is driven to oscillate. The ends of the bandknife are connected to a string. The bandknife and the string together form an endless loop comprising two loop portions merging into each other. The guiding of this loop requires at least six pulleys formed as bandknife pulleys and string pulleys. Also there, the loop is guided around pulleys deflecting the bandknife or the string alternately into one direction and a direction opposite thereto.
Further, DE 34 44 612 C2 discloses a contour cutting machine wherein the workpiece table comprises two conveyor belts arranged in a common plane, which are driven synchronously and form a gap for the passage of a cutting wire. The cutting wire is guided around four pulleys which are arranged on a frame adapted to be displaced and pivoted in its entirety. The cutting wire guiding path forms a single closed loop. When performing a contour cutting process, the whole frame, having a large mass moment of inertia, has to be moved.